Reactive Hot Melt Adhesive

ABSTRACT

The present disclosure relates to silane reactive hot melt adhesive compositions including acid functional wax and basic functional wax; the production of such adhesives; and the use of such adhesives. The silane reactive hot melt adhesive compositions have improved green strength as compared to silane reactive hot melt adhesive compositions without the acid functional wax and basic functional wax.

FIELD

This invention relates to silane reactive hot melt adhesive compositions having improved green strength, the production of such adhesives and the use of such adhesives.

BACKGROUND

Hot melt adhesive compositions are solid at room temperature but, upon application of heat, melt to a liquid or fluid state in which molten form they are applied to a substrate. On cooling, the adhesive composition regains its solid form. The hard phase(s) formed upon cooling of the adhesive composition impart all of the cohesion (strength, toughness, creep and heat resistance) to the final bond. Hot melt adhesive compositions are thermoplastic and can be heated to a fluid state and cooled to a solid state repeatedly. Hot melt adhesive compositions do not include water or solvents.

Curable or reactive hot melt adhesive compositions are also solid at room temperature and, upon application of heat, melt to a liquid or fluid state in which molten form they are applied to a substrate. On cooling, the adhesive composition regains its solid form. The phase(s) formed upon cooling of the adhesive composition and prior to curing impart initial or green strength to the bond. The adhesive composition will cure by a chemical crosslinking reaction upon exposure to suitable conditions such as exposure to moisture. Before curing the adhesive composition remains thermoplastic and can be remelted and resolidified. Once cured, the adhesive composition is in an irreversible solid form and is no longer thermoplastic. The crosslinked adhesive composition provides strength, toughness, creep and heat resistance to the final bond. Hot melt curable adhesive compositions can provide higher strength and heat resistance compared to non-curable hot melt adhesive compositions.

The ability of a reactive hot melt adhesive composition to cool so that the solidified but non-crosslinked composition can quickly bond parts together is called green strength. An adhesive composition that quickly develops green strength is desirable in commercial operations as it allows bonded parts to be further processed quickly. Reactive hot melt adhesive compositions will cure under appropriate conditions such as exposure to moisture so that strength of the adhesive bond between parts will continue to rise. A high cured strength is desirable in commercial operations as it allows stressed parts to be bonded.

In some applications such as roller coating the adhesive composition is melted in the reservoir of roller coating equipment and applied as a thin film by a roller to a substrate. The molten adhesive composition in the roller coating equipment will react with moisture in the air and begin to crosslink. At some time the cross linking will progress to a point where the equipment must be shut down so the partially cross linked adhesive composition can be removed and the equipment cleaned. Failure to clean the partially crosslinked adhesive composition can lead to application difficulties and ultimately to the composition fully curing and solidifying in the equipment, requiring equipment shutdown and extensive disassembly. Thus, a long working life is desirable.

Some adhesive compositions will form a string between the just coated substrate and application equipment such as a roller coater when the coated substrate is removed from the equipment. These hot adhesive strings are undesirable as they accumulate on the equipment and require cleaning. Thus, minimizing stringing is desirable. These requirements are conflicting. An adhesive composition that crosslinks quickly to provide cured strength will have a short working life. An adhesive composition that crosslinks slowly will have a long working life but will develop strength more slowly, slowing subsequent commercial operations. It can be difficult to find one reactive hot melt adhesive composition that has a commercially desirable combination of green strength, cured strength, working life and stringing

The majority of reactive hot melts are moisture-curing urethane hot melt compositions. The reactive components of urethane hot melt compositions consist primarily of isocyanate terminated polyurethane prepolymers containing urethane groups and reactive isocyanate groups that react with surface or atmospheric moisture to chain extend and form a new polyurethane polymer. Polyurethane prepolymers are conventionally obtained by reacting diols with diisocyanates. Upon cooling the isocyanate groups in the polyurethane prepolymer react with moisture from the environment to form a crosslinked irreversible solid bond.

Moisture-curing urethane hot melt adhesive compositions have certain disadvantages. One disadvantage is the residual monomer content of polyisocyanates, more particularly the more volatile diisocyanates. Some moisture-curing urethane hot melt adhesive compositions can contain significant amounts of unreacted monomeric diisocyanates. At the hot melt application temperature (typically at 100° C. to 170° C.) monomeric diisocyanates have a considerable vapor pressure and may be partly expelled in gaseous form. The isocyanate vapors may be toxic, irritating and have a sensitizing effect, so that precautionary measures have to be taken in the application process.

Silane reactive hot melt adhesive compositions have been developed to avoid disadvantages of isocyanate reactive hot melt compositions. Silane reactive hot melt adhesive compositions are also solid at room temperature and, upon application of heat, melt to a liquid or fluid state in which molten form they are applied to a substrate. On cooling, the composition regains its solid form. Silane reactive hot melt adhesive compositions are based on silane modified polymers that comprise moisture reactive silane groups that form siloxane bonds when exposed to moisture such as in the atmosphere. Silane reactive hot melt adhesive compositions can be free of residual isocyanate monomers and isocyanate functionality. Silane reactive hot melt adhesive compositions offer good cured adhesion and since there is no isocyanate there are no concerns about emission of isocyanate monomer vapor. However, silane reactive hot melt adhesive compositions develop green strength slower than reactive polyurethane hot melt adhesive compositions.

There remains a need for a silane reactive hot melt adhesive composition that has a desirable combination of properties for commercial use including quick development of green strength, a long working life and high final (cured) strength.

BRIEF SUMMARY

It has been discovered that a silane reactive hot melt adhesive composition comprising a silane modified polymer; an effective amount of basic functional wax; and optionally, an effective amount of acidic functional wax develops green strength more quickly and has an extended working life and higher final strength after cure as compared to the same silane modified hot melt adhesive composition with no functional wax or the same silane modified hot melt adhesive composition with only acidic functional wax. One embodiment is directed to a silane reactive hot melt adhesive composition comprising a silane modified polymer, an effective amount of acidic functional wax, an effective amount of basic functional wax and a silane adhesion promoter. Preferably, the silane adhesion promoter is an aminosilane adhesion promoter.

Another embodiment is directed to a method of increasing the development of green strength in a silane reactive hot melt adhesive composition by adding an effective amount of acidic functional wax and an effective amount of basic functional wax.

Another embodiment is directed to a method for bonding materials together which comprises applying the silane reactive hot melt adhesive composition in a molten form to a first substrate, bringing a second substrate in contact with the molten composition applied to the first substrate, and subjecting the applied composition to conditions which will allow the composition to cool and cure to an irreversible solid form, said conditions comprising moisture.

Another embodiment is directed to an article of manufacture comprising a substrate bonded to cured reaction products of a silane reactive hot melt adhesive composition prepared from a silane modified polymer and controlled ranges of both acidic functional wax and basic functional wax.

The disclosed compounds include any and all isomers and stereoisomers. In general, unless otherwise explicitly stated the disclosed materials and processes may be alternately formulated to comprise, consist of, or consist essentially of, any appropriate components, moieties or steps herein disclosed. The disclosed materials and processes may additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any components, materials, ingredients, adjuvants, moieties, species and steps used in the prior art compositions or that are otherwise not necessary to the achievement of the function and/or objective of the present disclosure.

When the word “about” is used herein it is meant that the amount or condition it modifies can vary some beyond the stated amount so long as the function and/or objective of the disclosure are realized. The skilled artisan understands that there is seldom time to fully explore the extent of any area and expects that the disclosed result might extend, at least somewhat, beyond one or more of the disclosed limits. Later, having the benefit of this disclosure and understanding the concept and embodiments disclosed herein, a person of ordinary skill can, without inventive effort, explore beyond the disclosed limits and, when embodiments are found to be without any unexpected characteristics, those embodiments are within the meaning of the term about as used herein.

DETAILED DESCRIPTION

The disclosures of all documents cited herein are incorporated in their entireties by reference.

As used herein, “irreversible solid form” means a solid form wherein the silane reactive hot melt adhesive composition has crosslinked to produce a cured, thermoset, insoluble material.

The silane reactive hot melt adhesive composition comprises one or more silane modified polymers. The silane modified polymer has an organic backbone, bearing one or more terminal or pendant silane or alkoxylated silane groups. The silane groups are hydrolyzed by water to silanol groups, which can condense with each other or with reactive species on the adherent surfaces. The silane modified polymer may be prepared with one or more of a variety of polymer backbones such as polyurethane (for example derived from Baycoll 2458 from Bayer), polyether, polyester, polyetherester, polyesterether, polyolefin, polycaprolactone, polyacrylate, polybutadiene, polycarbonate, polyacetal, polyester amide, polythioether, polyolefin and the like. Advantageous backbones for the silane modified polymer include polyurethane and polyether and especially acrylate modified polyether (prepared for instance as described in U.S. Pat. No. 6,350,345, the contents of which are incorporated reference). The silane modified polymer organic backbone can be free of silicon atoms. The silane modified polymer can be a low modulus silane modified polymer having a Young's modulus for the cured, neat polymer lower than 50 psi; a high modulus silane modified polymer having a Young's modulus for the cured, neat polymer equal or greater than 50 psi; or a combination of low modulus silane modified polymer and high modulus silane modified polymer.

The silane modified polymer can be represented by the formula

R-[A-Si(C_(x)H_(2x+1))_(n)(OC_(y)H_(2y+1))_(3-n)]_(z)

wherein R is the organic backbone;

A is a linkage that links the silane to polymer backbone R;

n=0, 1 or 2;

x and y are, independently a number from 1 to 12.

The number of silane groups z will preferably be more than one per molecule (to generate a fully cured network), and more preferably at least two per molecule. More preferably, the silane functional polymer is telechelic or end-functionalized, where most or all the ends are silane functional. The number of silyl ether groups per silane end group, 3-n, is preferably 2 or 3 (n=1 or 0). The silane reactive hot melt adhesive composition cures during exposure to water or moisture, when the silane groups are hydrolyzed to silanol groups which can condense with each other or with reactive species on the surfaces to be bonded.

Silane modified polymers are commercially available, for example, from Momentive Performance Material under the trade name SPUR, from Henkel Corporation under the trade name FLEXTEC and from Kaneka Corporation under the trade name MS polymer and SILYL polymer.

The silane modified polymer is advantageously liquid at room temperature.

The amount of silane modified polymer in the composition will depend on its molecular weight and functionality, but will typically be from 20-80 wt %, advantageously 25-60 wt %, and more advantageously from 30-50 wt %, based on the total weight of the adhesive composition.

The silane reactive hot melt adhesive composition can optionally comprise a controlled amount of acidic functional wax. By “acidic functional wax” it is meant that the wax includes a functional moiety that is acidic. The acidic functional wax can have terminal or pendant acidic functional moieties.

Ullmann's Encyclopedia of Industrial Chemistry, the contents of which are incorporated by reference herein, describes waxes. Examples of types of waxes that may be used include natural waxes, partially synthetic waxes and fully synthetic waxes. Natural waxes are formed through biochemical processes and are products of animal or plant metabolism. Partially synthetic waxes are formed by chemically reacting natural waxes. Fully synthetic waxes are prepared by polymerizing low molar mass starting materials such as carbon, methane, ethane or propane. The two main groups of fully synthetic waxes are the Fischer-Tropsch waxes and polyolefin waxes such as polyethylene wax, polypropylene wax and copolymers thereof.

Acidic functional groups are added to the wax molecule by, for example, grafting synthetic waxes with an acidic moiety such as carboxylic acid or maleic anhydride or by cleavage of the esters and/or oxidation of the alcohols in partially synthetic waxes. Acidic functional waxes can have a saponification number (mg KOH/gm wax) of less than about 90 and more advantageously from about 5 to about 30. Some useful acid functional maleated waxes can have about 50% to about 95% of maleic anhydride moieties bound to the wax backbone with the remaining maleic anhydride content not bound to the wax backbone.

Acidic functional waxes are available commercially, for example from Clariant International Ltd, Switzerland; EPChem International Pte Ltd, Singapore; Honeywell International Inc., U.S. and Westlake Chemical Corp, U.S. Advantageous acid functional waxes are the maleated polypropylene waxes. One useful maleated polypropylene wax is A-C 1325P available from Honeywell International Inc.

The use of acid functional wax in the silane reactive hot melt adhesive composition is optional. Advantageously, the silane reactive hot melt adhesive composition will contain an effective amount of acid functional wax. An effective amount of acid functional wax is the amount of acid functional wax that will increase green strength of a silyl reactive hot melt adhesive composition without deleteriously degrading other properties of that composition. Surprisingly, while some amount of wax is required to more quickly provide green strength to the silane reactive hot melt adhesive composition the use of too much wax can deleteriously degrade properties of the composition such as cured strength. Thus, the amount of acid functional wax in the silane reactive hot melt adhesive composition must be kept in a controlled range. The silane reactive hot melt adhesive composition will contain 0.1 wt % to about 15 wt % of acid functional wax based on the total weight of the adhesive composition. Advantageously, the silane reactive hot melt adhesive composition will contain 0.1 wt % to about 8 wt % or even 0.1 wt % to about 4 wt % of acid functional wax based on the total weight of the adhesive composition.

The silane reactive hot melt adhesive composition comprises an effective amount of basic functional wax. By “basic functional wax” it is meant that the wax includes at least one functional moiety that is basic, for example amide moieties or amine moieties. The basic functional wax can have terminal, within the backbone, or pendant basic functional moieties. Basic functional groups are added to the wax molecule by, for example, grafting synthetic waxes with a basic moiety such as amine or amide. Basic functional groups can also be introduced by reacting molecules with basic functionality into the wax molecule.

Basic functional waxes are available commercially, for example from Honeywell International Inc., U.S. and Vertellus Inc., Greensboro, N.C. and Crayvallac Inc. Advantageous basic functional waxes are the amine and amide functional waxes. Useful basic functional waxes include ACumist from Honeywell International Inc. and Paricin 220 from Vertellus Performance Materials Inc, etc.

The silane reactive hot melt adhesive composition will contain an effective amount of basic functional wax. Surprisingly, addition of basic functional wax to reactive hot melt adhesive composition comprised of a silane modified polymer and acid functional wax allows the resulting composition to more quickly provide green strength as compared to the reactive hot melt adhesive composition without the basic wax.

An effective amount of basic functional wax is the amount of basic functional wax that will increase green strength of a reactive hot melt adhesive composition comprised of a silane modified polymer and acid functional wax without deleteriously degrading other properties of that composition. Surprisingly, while some amount of basic functional wax is required to improve green strength of the silane reactive hot melt adhesive composition the use of too much basic functional wax appears to deleteriously degrade properties of the composition such as cured strength. Thus, the amount of basic functional wax in the silane reactive hot melt adhesive composition must be kept in a controlled range. The silane reactive hot melt adhesive composition will contain about 0.05 wt % to about 8 wt % of basic functional wax based on the total weight of the adhesive composition. Advantageously, the silane reactive hot melt adhesive composition will contain about 0.2 wt % to about 4 wt % of basic functional wax based on the total weight of the adhesive composition. More advantageously, the silane reactive hot melt adhesive composition will contain about 0.2 wt % to about 2 wt % of basic functional wax based on the total weight of the adhesive composition.

In some embodiments the ratio of acidic functional wax to basic functional wax (R_(A:B)) is in the range of 0:1 to 10:1, or simply 0 to 10. More preferably, R_(A:B) is in the range of 1.5 to 2.5. While ratios outside of this range are useful, this ratio of acidic functional wax to basic functional wax provides a surprisingly improved effect to green strength of the silane reactive hot melt adhesive composition balanced with good final adhesion strength.

The silane reactive hot melt adhesive composition can optionally comprise tackifier. The choice of tackifier will depend on the backbone of the silane modified polymer. The tackifier choices include natural and petroleum-derived materials and combinations thereof as described in C. W. Paul, “Hot Melt Adhesives,” in Adhesion Science and Engineering-2, Surfaces, Chemistry and Applications, M. Chaudhury and A. V. Pocius eds., Elsevier, New York, 2002, p. 718, incorporated by reference herein.

Useful tackifier for the adhesive composition of the invention includes natural and modified rosin, aromatic tackifier or mixtures thereof. Useful natural and modified rosins include gum rosin, wood rosin, tall oil rosin, distilled rosin, hydrogenated rosin, dimerized rosin, resinates, and polymerized rosin; glycerol and pentaerythritol esters of natural and modified rosins, including, for example as the glycerol ester of pale, wood rosin, the glycerol ester of hydrogenated rosin, the glycerol ester of polymerized rosin, the pentaerythritol ester of hydrogenated rosin, and the phenolic-modified pentaerythritol ester of rosin. Examples of commercially available rosins and rosin derivatives that could be used to practice the invention include Sylvalite RE 110L, Sylvares RE 115, and Sylvares RE 104 available from Arizona Chemical; Dertocal 140 from DRT; Limed Rosin No. 1, GB-120, and Pencel C from Arakawa Chemical. One useful natural and modified rosin is a rosin ester tackifier such as KE-100, available from Arakawa Chemical Co. Another useful rosin ester tackifier is a Komotac 2110 from Komo Resins. Useful aromatic tackifiers include styrenic monomers, styrene, alpha-methyl styrene, vinyl toluene, methoxy styrene, tertiary butyl styrene, chiorostyrene, coumarone, indene monomers including indene, and methyl indene. Preferred are aromatic hydrocarbon resins that are phenolic-modified aromatic resins, C₉ hydrocarbon resins, aliphatic-modified aromatic C₉ hydrocarbon resins, C₉ aromatic/aliphatic olefin-derived and available from Sartomer and Cray Valley under the trade name Norsolene and from Rutgers series of TK aromatic hydrocarbon resins. Other useful aromatic tackifiers are alpha-methyl styrene types such as Kristalex 3100, Kristalex 5140 or Hercolite 240, all available from Eastman Chemical Co.

The tackifier component will usually be present in an amount of from about 15 wt ° A) to about 90 wt ° A), advantageously from about 20 wt % to about 50 wt %, more advantageously from about 25 wt % to about 40 wt %, based on the total weight of the adhesive composition. The rosin tackifier will be present from 0 to 30 wt %, advantageously from about 5 to about 25 wt %, based on the total weight of the adhesive composition. The aromatic tackifier will be present from 0 to about 60 wt %, advantageously from about 15 to about 40 wt %, based on the total weight of the adhesive composition.

The silane reactive hot melt adhesive composition can optionally comprise an acrylic polymer or copolymer (acrylic polymer). The acrylic polymer can improve green strength of the cooled hot melt adhesive composition. The acrylic polymer can be either a silane-reactive polymer or non-reactive polymer. A silane reactive polymer comprises groups such as carboxylic acid, amine, thiol and hydroxyl that react with silane moieties. A preferred silane reactive group is carboxylic acid. The number of groups should be sufficient such that a significant amount, at least 5%, of the acrylic polymer is grafted to the silane modified polymer via the silane groups. A non-silane reactive acrylic polymer does not include groups that are reactive with the silane modified polymer.

One useful reactive acrylic polymer is Elvacite 2903 from INEOS Acrylics. Elvacite 2903 is a solid acrylic copolymer comprising acid and hydroxyl groups, has an acid number 5.2 and hydroxyl number of 9.5.

The amount of solid acrylic polymer in the adhesive composition will depend on a number of factors, including the glass transition temperature and molecular weight of the acrylic polymer, but will typically be present in an amount of from about 10 to about 45 wt %, based on the total weight of the adhesive composition.

The silane reactive hot melt adhesive composition can optionally comprise a catalyst. Suitable curing agents for the silane groups are described in U.S. Patent Publication No. 2002/0084030, and incorporated by reference herein. Exemplary catalysts includes bismuth compounds such as bismuth carboxylate; organic tin catalysts such as dimethyltin dineodecanoate, dibutyltin oxide and dibutyltin diacetate; titanium alkoxides (TYZOR® types, available from DuPont); tertiary amines such as bis (2-morpholinoethyl) ether, 2,2′-Dimorpholino Diethyl Ether (DMDEE) and triethylene diamine; zirconium complexes (KAT XC6212, K-KAT XC-A209 available from King Industries, Inc.); aluminum chelates (K-KAT 5218, K-KAT 4205 available from King Industries, Inc.), KR types (available from Kenrich Petrochemical, Inc.); and other organometallic compounds based on Bi, Sn, Zn, Co, Ni, and Fe and the like. The level of catalyst in the silane reactive hot melt adhesive composition will depend on the type of catalyst used, but can range from about 0.05 to about 5 wt %, advantageously from about 0.1 to about 3 wt % and more advantageously from about 0.1 to about 2 wt %, based on the total weight of the adhesive composition.

The silane reactive hot melt adhesive composition can optionally comprise a moisture scavenger to extend pot life, such as vinyl trimethoxy silane or methacryloxypropyltrimethoxysilane. The level of moisture scavenger employed can be from 0 to 3% and preferably from 0 to 2%, based on the total weight of the adhesive composition.

The adhesive composition can comprise an adhesion promoter or coupling agent which promotes bonding of the composition to a substrate. Examples are described in: Michel J. Owen, “Coupling agents: chemical bonding at interfaces”, in Adhesion Science and Engineering-2, Surfaces, Chemistry and Applications, M. Chaudhury and A. V. Pocius eds., Elsevier, New York, 2002, p. 403, incorporated by reference herein. Preferred adhesion promoters include organo-silanes which can link the silane-functional polymer to the surface such as amino silanes and epoxy silanes. Some exemplary aminosilane adhesion promoters include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-(2-aminoethyl-3-aminopropyl)trimethoxysilane, 3-aminopropylmethyldiethoxysilane, 4-amino-3,3-dimethylbutyltrimethoxysilane, N-(n-butyl)-3-aminopropyltrimethoxysilane, 1-butanamino-4-(dimethoxymethylsilyl)-2,2-dimethyl, (N-cyclohexylaminomethyl)triethoxysilane, (N-cyclohexylaminomethyl)-methyldiethoxysilane, (N-phenylaminoethyl)trimethoxysilane, (N-phenylaminomethyl)-methyldimethoxysilane or gamma-ureidopropyltrialkoxysilane. Particularly preferred amino silanes include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane. Some exemplary epoxy silane adhesion promoters include 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane or beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. Other silane adhesion promoters include mercaptosilanes. Some exemplary mercaptosilane adhesion promoters include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane or 3-mercaptopropyltriethoxysilane. The level of adhesion promoter employed can be from 0 to 10 wt %, preferably 0.1 wt % to 5 wt % and more preferably 0.2 wt % to 3 wt % based on the total weight of the adhesive composition. The adhesion promoter may act as a crosslinker or, if more reactive to moisture than the silane modified polymer, can also serve as a moisture scavenger.

The silane reactive hot melt adhesive composition can optionally comprise conventional additives known to a person skilled in the adhesive art. Conventional additives which are compatible with the disclosed adhesive composition may simply be determined by combining a potential additive with the composition and determining if they remain homogenous. Non-limiting examples of suitable additives include, without limitation, fillers, plasticizers, defoamers, rheology modifiers, air release agents and flame retardants.

The total level of additives will vary depending on amount of each particular additive needed to provide the silane reactive hot melt adhesive composition with desired properties. The level of additives can be from 0 to 50 wt % based on the total weight of the adhesive composition.

An exemplary silane reactive hot melt adhesive composition is shown below.

range preferred range component (wt %) (wt %) silane modified polymer 20-80 30-60 acidic functional wax 0.1-15  0.5-8  basic functional wax 0.1-8  0.2-4  ratio acid functional wax:basic ≧0  0-10 functional wax (R_(A:B)) natural and modified rosin tackifier  0-30  3-20 aromatic tackifier  0-60 10-35 acrylic polymer 10-45 15-35 catalyst 0.05-5   0.05-2   moisture scavenger 0-3  0-1.5 adhesion promoter  0-10 0.1-2  additives  0-50  5-40 R 0.1-1.8 0.3-1.2

The silane reactive hot melt adhesive composition is preferably free of water and/or solvent in either the solid and/or molten form.

The silane reactive hot melt adhesive composition can be prepared by mixing the tackifier, waxes and other non-reactive components with heat until homogeneously blended. The mixer is placed under vacuum to remove moisture followed by heated mixing of the reactive components.

The silane reactive hot melt adhesive compositions can be used to bond articles together by applying the hot melt adhesive composition in heated, molten form to a first article, bringing a second article in contact with the molten composition applied to the first article. After application of the second article the silane reactive hot melt adhesive composition is subjected to conditions that will allow it to solidify, bonding the first and second articles. Solidification occurs when the liquid melt is subjected to a temperature below the melting point, typically room temperature. The phase(s) formed upon cooling of the adhesive composition and prior to curing impart initial or green strength to the bond. After solidification the adhesive is exposed to conditions such as surface or atmospheric moisture that crosslink and cure the solidified composition to an irreversible solid form.

The silane reactive hot melt adhesive compositions are useful for bonding articles composed of a wide variety of substrates (materials), including but not limited to wood, metal, polymeric plastics, glass and textiles. Non-limiting uses include use in the manufacture of footwear (shoes), use in manufacture of windows and doors including entry doors, garage doors and the like, use in the manufacture of panels, use in bonding components on the exterior of vehicles, and the like.

Application temperatures of the silane reactive hot melt adhesive compositions are determined by the thermal stability of the composition and the heat sensitivity of the substrates. Preferred application temperatures are above 120° C. and below 170° C., more preferably below 150° C., and most preferably below 140° C.

The silane reactive hot melt adhesive compositions may be then applied in molten form to substrates using a variety of application techniques known in the art. Examples includes hot melt glue gun, hot melt slot-die coating, hot melt wheel coating, hot melt roller coating, melt blown coating, spiral spray and the like. In preferred embodiments the hot melt adhesive composition is applied to a substrate using hot melt roller coater or extruded onto a substrate.

The invention is further illustrated by the following non-limiting examples.

EXAMPLES

The following tests were used in the Examples.

Acid number (ASTM D-1386)—Standard Test Method for Acid Number (Empirical) of Synthetic and Natural Waxes

Saponification number (ASTM D-1387)—Standard Test Method for Saponification Number (Empirical) of Synthetic and Natural Waxes

Viscosity—viscosity was measured using a Brookfield digital viscometer with a Thermosel heating unit, small sample adapter, 27 spindle, (and 13 chamber.) Desirably, viscosity of the silane reactive hot melt adhesive composition should be about 5,000 to 25,000 cps at 250° F.

Final (cured) strength by Lap Shear Adhesion Test (TLS)—The adhesive was applied to a clean PVC substrate. A stainless steel drawdown applicator (BYK-Gardner) was used to obtain a controlled thickness of 0.030 inches. Glass bead spacers 0.020 in thickness were sprinkled on top of the adhesive layer to control the final bondline thickness. Clean glass strips 1 inch by 3 inches were bonded to the applied adhesive with an overlapping area of 1 inch by 1 inch using hand pressure. The finished bonds were conditioned at 72° F./50% RH for two weeks before testing to allow for full moisture cure. Tensile samples were pulled along the long axis at 0.5 inches/min until failure in an Instron tensile test machine either at room temperature or immediately after heating the sample for 0.5 hr in an oven at 180° F. Desirably, on glass to PVC substrates, final strength of the silane reactive hot melt adhesive composition should be greater than 60 psi at room temperature and greater than 20 psi at 180° F.

Green Strength and strength development by TLS—Lap shear bonds were made and tested as described above, but were tested during cure process (2 hours, 1 day and one week) after bonding. This test characterizes the ability of the bonded structure to survive handling in manufacture prior to full cure. Hot melts have the advantage of high strength in the green state which minimizes working inventory.

The following materials were used in the Examples.

A-C 1325P a maleated polypropylene wax available from Honeywell International Inc. The manufacturer states that A-C 1325P has 78% bound maleic anhydride; a saponification number of 18 mg KOH/gm wax; and a viscosity of 1600 cps at 190° C.

Paricine 220 is N-(2-hydroxyethel) 12-hydroxystearamide available from Vertellus Inc., Greensboro, N.C.

MAX 951 is a low modulus silane terminated polyether, commercially available from Kaneka Corp.

Elvacite 2903 is a solid acrylic polymer, available from Ineos Acrylics.

Kristalex 3100 is an alpha-methyl styrene tackifier, available from Eastman Chemical Co.

A1110 is an adhesion promoter, available from Momentive Performance Materials.

KBM903 is an adhesion promoter, available from Shin Etsu Silicone.

A515 is an air release agent, available from BYK Chemie.

Teckros H95 is a hydrogenated rosin ester tackifier, available from Teckrez, Inc.

Reaxis C233 is a tin catalyst available from Reaxis Inc.

EB50 866 is a UV absorber available from BASF.

Example 1

Samples of silane reactive hot melt adhesive compositions were prepared according to the following table. The air release agent, UV absorber, acrylic polymer, tackifiers and any functional wax were combined, heated to about 300° F. and stirred until homogeneous. Vacuum was applied to remove any water and the temperature was lowered to about 270° F. Silane modified polymer was added and vacuum mixed until homogeneous. The adhesion promoter and catalyst were added and vacuum mixed until homogeneous. The final adhesive was poured into a container, sealed under nitrogen and cooled to room temperature.

Sample A is a comparative example with no acid functionalized wax and no basic functional wax. Sample B is a comparative example with 8 parts (2.2%) acid functionalized wax and no basic functional wax. Samples 1-4 are exemplary inventive examples with 8 parts acid functionalized wax and varying amounts of basic functional wax. Sample 5 is an example with 4 parts of basic functional wax and no acid functional wax.

A B 5 1 2 3 4 Material silane modified 140 140 140 140 140 140 140 polymer¹ tackifier² 52 52 52 52 52 52 52 acrylic polymer³ 92 92 92 92 92 92 92 tackifier⁴ 52 52 52 52 52 52 52 UV absorber⁵ 3 3 3 3 3 3 3 air release agent⁶ 3 3 3 3 3 3 3 adhesion promoter⁷ 4 4 4 4 4 4 4 catalyst⁸ 4 4 4 4 4 4 4 acid functional wax⁹ 0 8 0 8 8 8 8 basic functional 0 0 4 0.8 1.6 4 8 wax¹⁰ total (grams) 350 358 355 359.8 361.6 365 370 (R_(A:B)) — — — 10 5 2 1 ¹Max 951 ²Teckros H95 ³Elvacite 2903 ⁴Kristflex 3100 ⁵EB50 866 ⁶A515 ⁷A-1110 ⁸Reaxis C233 ⁹A-C 1325 ¹⁰Paricin 220 Property (R_(A:B)) — — — 10 5 2 1 R Clarity Tr¹ Tr Tr Tr Tr Tr Tr Viscosity (cps 8975 18900 20600 17800 17000 22050 19750 @ 250° F.) Shore A hardness 63.3 70 65 80 78.7 78.3 80 Strength TLS (psi) glass/PVC 2 hours 25 22 40.6 31 32 46 40 failure mode¹ CF AF CF AF AF CF CF 24 hours 26 50 56 45 41 68 46 failure mode AF AF CF AF CF CF CF 168 hours 98 102 99.6 85 76 101 111 failure mode AF AF CF AF AF AF AF Final Strength TLS (psi) glass/PVC Room temperature 166.8 142.7 102 120.8 130 125.1 99 failure mode AF AF AF AF AF AF AF 180° F. 36.2 37 17.1 49.6 36 25.5 23.4 failure mode AF AF AF AF AF AF AF ¹Tr indicates sample was translucent 2 AF = predominately adhesive failure mode; CF = predominately cohesive failure mode. The transition from a cohesive failure mode to an adhesive failure mode indicates crosslinking of the adhesive.

Sample 3 provides the best performance, having the best results in green strength and setting speed, as shown by the adhesion results at 2 hours, 24 hours and 168 hours. The other samples have lower green strength or weaker final adhesion strength.

Many modifications and variations of this invention can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. The specific embodiments described herein are offered by way of example only, and the invention is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. 

1. A silane reactive hot melt adhesive composition comprising: a silane modified polymer; 0.1 wt % to 15 wt % of acid functional wax based on weight of the adhesive composition; and 0.05 wt % to 8 wt % of basic functional wax based on weight of the adhesive composition.
 2. The silane reactive hot melt adhesive composition of claim 1, comprising 0.1 wt % to 2 wt % of basic functional wax based on weight of the adhesive composition.
 3. The silane reactive hot melt adhesive composition of claim 1 wherein the ratio of acidic functional wax to basic functional wax (R_(A:B)) is preferably in the range of 0 to preferably 1.5 to 2.5.
 4. The silane reactive hot melt adhesive composition of claim 1 further comprising an aminosilane adhesion promoter.
 5. The silane reactive hot melt adhesive composition of claim 1 further comprising an aminosilane adhesion promoter wherein the molar ratio of acid functionality from the acid functional wax and amino functionality of the aminosilane (R) is equal or less than 1 preferably 0.3 to 1.2.
 6. The silane reactive hot melt adhesive composition of claim 1 being free of isocyanate functionality.
 7. The silane reactive hot melt adhesive composition of claim 1 further comprising one or more of a tackifier selected from rosin ester, hydrogenated hydrocarbon, aromatic tackifier or mixtures thereof; an acrylic polymer; and a catalyst.
 8. The silane reactive hot melt adhesive composition of claim 1, wherein the silane modified polymer comprises a plurality of terminal silyl groups each independently having a formula of A-Si(C_(x)H_(2x+1))_(n)(OC_(y)H_(2y+1))_(3-n), wherein A is a linkage to the polymer backbone; x is 1 to 12; y is 1 to 12; and n is 0, 1 or 2; and the silyl group of the silane modified liquid polymer is end-functionalized.
 9. The silane reactive hot melt adhesive composition of claim 1, wherein the silane modified polymer has a backbone structure selected from polyurethane, polyether, polyester, polyacrylate or polyolefin.
 10. The silane reactive hot melt adhesive composition of claim 1, wherein the silane modified polymer has a formula R-[A-Si(C_(x)H_(2x+1))_(n)(OC_(y)H_(2y+1))_(3-n)]z wherein R is an organic backbone of the silane modified polymer without silicon atoms, A is a linkage that links the silane group to the polymer backbone R. n=0, 1 or 2; x and y are, independently a number from 1 to 12; and z is at least one.
 11. The silane reactive hot melt adhesive composition of claim 1, wherein the silane modified polymer comprises a plurality of telechelic silyl groups each independently having a formula of A-Si(C_(x)H_(2x+1))_(n)(OC_(y)H_(2y+1))_(3-n), wherein A is a linkage to the polymer backbone; x is 1 to 12; y is 1 to 12; and n is 0, 1 or
 2. 12. The silane reactive hot melt adhesive composition of claim 1 being free of water and solvent.
 13. A method of applying a silane reactive hot melt adhesive composition comprising: providing the silane reactive hot melt adhesive composition of claim 1 in solid form at room temperature; heating the silane reactive hot melt adhesive composition to a molten state at the point of use; applying the molten silane reactive hot melt adhesive composition to a first substrate; bringing a second substrate in contact with the molten adhesive composition applied to the first substrate; cooling the applied molten adhesive composition to, a solid state; subjecting the cooled adhesive composition to conditions sufficient to irreversibly cure the cooled adhesive composition to form a bond between the first and second substrates.
 14. The method of claim 16 wherein the step of applying the molten silane reactive hot melt adhesive composition is selected from spray application, extrusion, and roll coating.
 15. An article of manufacture comprising cured reaction products of the silane reactive hot melt adhesive composition of claim
 1. 